Nerve Growth Factor and Gangliosides Stimulate the Release of Glycoproteins from PC 12 Pheochromocytoma Cells

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Abstract
PC 12 pheochromocytoma cells in monolayer cultures secrete increased amounts of glycoproteins into the medium following the addition of nerve growth factor (NGF) or of brain gangliosides. After a 48‐h incubation with 50 ng/ml NGF there is approximately a twofold increase in the total [14C] glucosamine‐labeled, ethanol‐precipitable cellular material released into the medium. Between 30 and 50% of the radioactivity is associated with a glycoprotein (Gpl) of molecular weight of 52,000; the remaining radioactivity is distributed between five and six major bands. Only a small amount (10%) is associated with a glycoprotein of Mr > 200,000 which might correspond to the NGF‐induced large external glycoprotein. A substantial increase in the release of the glycoproteins is also seen on the addition of a variety of gangliosides in‐ cluding asialo GMl. This increase is independent of the presence of NGF. GMl and GDlB/GTlb but not GDla stimulate release above the levels seen in the presence of NGF. Addition of GDla (2 (μg/ml) enhances selectively the release of various glycoproteins between 2.6‐and 8‐fold. The pattern of glycoprotein secretion is similar to that seen with NGF, although Gp2 (Mr 78,000) is more abundant. Stimulation of release by GDia is not accompanied by neurite outgrowth, suggesting that the glycoproteins are not directly associated with neuritogenesis. The release of these glycoproteins following the addition of NGF or gangliosides may relate to the neurotrophic properties that these two entirely different ligands exert on PC12 cells.